This invention concerns providing cellular polymers suitable for use in products for absorbing body fluids such as for example, sanitary napkins, catamenial tampons, diapers, bandages, surgical dressings and the like. Such materials, commonly referred to as foams have already been considered for use in such products and various polymers and processes have been suggested as suitable including, for example, polyurethane foams, polyester foams and cellulose foams.
While these foams, in the main, have been capable of absorbing body fluids to varying degrees, their properties having fallen short of those preferred for products such as diapers, sanitary napkins and the like. In general these prior art foams lack the characteristics of efficient wicking and good liquid retention. In many cases the foams are either not compressible or if compressible, not readily expandable when wetted.
A major forward step in the art of providing foams for use in body fluid absorbing products is disclosed in my copending U.S. patent application Ser. No. 485,782, filed on Apr. 18, 1983 for Resilient Cellular Polymers from Amine Terminated Poly(oxyalkylene) and Polyfunctional Epoxides, the specification of which is incorporated herein by reference. As taught therein, a usable foam may be prepared by foaming the reaction product of amine terminated poly(oxyalkylene) and polyfunctional epoxides, provided that the poly(oxyalkylene) component comprises poly(ethylene oxide) and poly(propylene oxide) wherein the ratio of ethylene oxide groups to propylene oxide groups are within a critical range. The resulting foam is absorbent, exhibits good wicking properties, and is highly resilient.
While this latter described foam is useful for many purposes, improvement is still desired. Specifically, it is desirable to improve the water retention properties of foam when under the influence of pressure. This property is of great importance in such body fluid absorbent products as diapers and napkins which are worn by the user and, after being wetted, are subject to pressure by the body movements of the wearer. Further, while in some applications, the dry resiliency of these foams are advantageous as they provide a measure of comfort to the user, in other applications, dry resiliency is disadvantageous. For example, particularly in the case of sanitary napkins, panty shields, catamenial tampons, or the like, it is desirable to produce as thin a product as is possible. In this instance the preferred absorbent material would be one which is highly compressible in the dry state, i.e., capable of being compressed into a thin sheet or small cylinder, as for catamenial tampons, and then has the characteristic of expanding upon wetting, thereby providing the intercellular void volume for taking up the body fluid. The prior foams lack these properties. Further still, the latter described foams are the products of a rather limited class of polymers and because of economic or availability considerations, it is desirable to expand the class of suitable polymers for use in providing usable foam.
Accordingly, there is a need for improvement in providing foams for use in absorbing fluids and particularly for absorbing body fluids.